Technical Field
The present invention relates to a light source device that can change the wavelength of outgoing light, and can emit outgoing lights of various wavelengths from the same optical axis.
Background Art
In recent years, spectroscopic analysis using a laser light of two wavelengths or more has started to be put to practical use. For example, there is a method whereby, when detecting the concentration of a certain component, the difference in intensity between a wavelength absorbed by the component and transmitted light of a wavelength that is not absorbed is detected. This kind of two wavelength or more laser spectrometry is implemented utilizing not only absorption by a detected component, but also optical characteristics such as scattering and reflection.
With the heretofore described spectroscopic analysis using laser light, it is often the case that a laser diode is commonly used in measuring in an infrared region. In an infrared region, it is comparatively easy to fabricate a laser diode of any wavelength using a DFB structure, or the like.
Meanwhile, with, for example, spectroscopic analysis of a component inside a human body, or the like, there is a desire to carry out spectroscopic analysis using the wavelength of visible light. However, as no appropriate light source exists for visible light, it is difficult to implement the heretofore described spectroscopic analysis in these regions (in particular, 490 nm to 630 nm).
A method of obtaining a light source of visible light of 490 nm to 630 nm is commonly implemented using wavelength conversion. For example, in JP-A-2004-172314, there is described a method whereby visible light of two wavelengths is obtained by exciting a solid laser medium using a laser diode, generating two different kinds of fundamental wave, and subsequently converting the wavelengths with a non-linear crystal. As described in this document, in order that the optical axis is the same, spatial light coupling with a half mirror is used.
Also, as described in JP-A-2007-97629, plural visible lights having mutually differing wavelengths are obtained by generating plural fundamental waves using plural fiber amplifiers as laser media, and converting the wavelengths of the fundamental waves with a non-linear crystal. As described in this document, in order that the optical axis is the same, a light switch configured of fiber is used.
With the technologies described in JP-A-2004-172314 and JP-A-2007-97629, plural fundamental waves are generated by exciting a laser medium, and the wavelengths of the fundamental waves are converted. When using a laser medium in this way, time is needed for a stimulated emission from the laser medium, meaning that modulation speed decreases.